Method of controlling the flow of absorbent according to the liquid level in a presaturation zone



Nov. 9, 1965 R. C. BRACKEN ETAL METHOD oF coNTRoLLING THE FLow oFABsoRBENT ACCORDING TO THE LIQUID LEVEL IN A PRESATURATION ZONE FiledApril 30, 1962 INVENTORS.

R. c. BRACKEN c. LsoMMERs HIGHOSBV M 14:77/ ATTORNEVS United StatesPatent 3,216,177 METHOD OF CONTROLLING THE FLOW OF ABSORBENT ACCORDINGT0 THE LIQUID LEVEL IN A PRESATURATION ZONE Robert C. Bracken and ClairL. Sommers, Bartiesville, Okla., assignors to Phillips PetroleumCompany, a corporation of Delaware Filed Apr. 30, 1962, Ser. No. 191,1321 Claim. (Cl. 55-18) This invention relates to control of a method forextraction of gasoline from natural gas. In one aspect it relates tocontrol of the operation of a steam turbine driven pump which transfersliquid absorbent from a presaturator zone to an absorption zoneoperating at a higher pressure than the pressure of the presaturatorzone.

Superheated steam is frequently employed for heat eX- change purposesfor heating fluids to temperatures well above the normal boiling pointof water. Such heat eX- changers sometimes exhaust steam in superheatedform and at pressures above atmospheric pressure. In plants in whichsuch exhaust steam is available, its use is frequently less expensivefor power purposes than electrical power. When such steam is notemployed for useful purposes, it may be Vented and, therefore, wasted.Such practice is ob- Viously to be avoided whenever possible.

An object of this invention is to provide a method for the `control of asystem for extraction of gasoline boiling range hydrocarbons from anatural gas. Another object of this invention is to provide means and amethod for the control of the operation of a steam driven turbine pumpwhich transfers liquid absorbent from a presaturator zone to anabsorption zone operating at a higher pressure than the pressure of thepresaturator zone. Another object of this invention is to provideapparatus for preventing the steam turbine driven pump from going on gasas the result of transfer of all liquid from the kettle section of thepresaturator. Other objects and advantages of this invention will berealized upon reading the following description, which, taken with theattached drawing, forms a part of this specification.

This invention comprises a method for throttling the flow of steam tothe steam turbine as a means for regulating the rate of pumping ofliquid absorbent from the kettle section of a presaturator zone to anabsorption zone operating at a higher pressure than the pressure of thepresaturator zone. The operation comprises sensing the liquid level inthe presaturator zone and as the level decreases throttling the flow -ofsteam to the steam turbine, and vice versa. Furthermore, the inventioninvolves upon sensing a liquid level in the presaturator which is apredeterrnined low level and in response to this predetermined low levelentirely closing off the flow of steam to the steam turbine so that theturbine driven pump will not go on gas, thereby tending to damage theturbine and pump from excessive speed.

The drawing illustrates, in diagrammatic form, an arrangement ofapparatus parts for carrying out the method of this invention.

In the drawing, reference numeral 11 identifies a conduit for passage offeed gas containing extractable hydrocarbons into an absorber 12.Conduit 13 passes unabsorbed or residue gas from absorber 12 to a pointof disposal as desired. Conduit 14 is for passage of enriched absorbentfrom absorber 12.

Rich absorbent flowing through conduit 14 is Vented by a first pressurereduction in the vent tank 15 with the Vented gases being passed througha conduit 16 and returned to the absorber 12. Partially Vented richabsorbent passes through a conduit 17 to a second vent tank 18, thegases from which pass through a conduit 42 with the liquid flowingthrough a conduit 19 to a third vent tank 20.

3,216,177 Patented Nov. 9, 1965 From this vent tank gases pass throughconduit 43 while the fully Vented absorbent passes through a conduit 21,through a heater 22 and thence through a conduit 23 for introductioninto a still-portion 25 of a dephlegmator-still 2.4. Gases stripped fromthe absorption liquid in still 25 pass upward into the dephlegmatorportion 26 for condensation of any vaporized absorbent. Gases and vaporsleave dephlegmator 26 through a conduit 27 and are condensed in acondenser 27a and pass to such disposal, as desired. The several ventingstages are at successively reduced pressures.

Stripped absorbent from the kettle section of still 25 leaves thisvessel by way of a conduit 29 provided with a cooler 30 and the cooledabsorbent is then passed into a lean oil surge storage tank 3. Condensedmaterial in dephlegmator 26 is removed therefrom through a conduit 28for such disposal as desired. When the condensate in dephlegrnator 26 issubstantially only absorption oil conduit 28 can be connected with thestill section 25 for return of the condensate to the main body ofabsorption oil. Fully stripped lens absorption oil from surge tank 31 ispassed therefrom by way of a conduit 32 with a portion thereof beingpassed through a conduit 37, the volume of which is regulated by a flowrecorder-controller 38. This absorbent passing through conduit 37 isintroduced into the upper portion of a reabsorber vessel 39. Ventedgases from vent tank 18 passing through conduit 42 are introduced intothe lower portion of the reabsorber 39, for recovery of desiredcondensable components. Vent gases flowing through conduit 43 areintroduced into an upper portion of still 25.

The enriched absorbent from reabsorber 39 containing recoveredcomponents is withdrawn therefrom by way of a conduit 41 and is combinedwith the main body of enriched absorption oil prior to introduction intovent tank 18. Unabsorbed gases from reabsorber 39 are passed by way of aconduit 40 and introduced into a presaturator vessel 44.

This presaturator vessel is intended to contact the reabsorber off gaseswith fully depleted lean absorption oil flowing through a conduit 45with rate of flow of the oil being controlled by a flowrecorder-controller 46. This lean absorbent is introduced into the upperportion of presaturator 44 and contacts the reabsorber off-gasestherein. Certain constituents desired to be retained in the off-gasesfrom the main absorber vessel 12 are absorbed in the presaturator. Insome instances and, in fact, in most instances, a manually operablevalve 35 is throttled somewhat in order to cause a pressure drop acrossthis valve so as to divert a portion of the 'lean oil pumped by pump 68through the reabsorber 39. Also a manually operable valve 36 is providedin conduit 32 so as to cause a pressure drop across the valve to force aportion of the lean absorption oil not required in reabsorber 39 to flowthrough conduit 45 into the presaturator vessel 44. In some instancesmanually operable valve 36 can be entirely closed or it can be merelythrottled to divert a portion of the oi'l through the presaturator.Thus, if some oil flows through valve 36 it is then combined with thepresaturator oil from conduit 53 and the combined stream is pumped by apump 34a driven by a steam turbine 34. The pumped oil flows on throughconduit 33 containing a check valve 67 and through a flow sensing devicesuch as an orifice plate assembly 58 and on into absorber 12.

Residue gas from absorber 12 as mentioned hereinabove leaves thisabsorber by way of a conduit 13 and this gas can, if desired, flowthrough a valve 52, a dehydrator apparatus 49 and on through a conduit50 for such use of a dehydrated gas, as desired. If however, it isdesired, all or a portion of the unabsorbed gas flowing through conduit13 can flow through a valve 51 in a conduit 48 and be combined with theoff-gas flowing through conduit 47 from the presaturator Vessel 44.

The control portion of the apparatus illustrated in the figure includesa liquid level sensing device 54, such as a float assembly.

The apparatus as herein described is a fully pneumatic apparatus whileit will be realized that electrical apparatus or combinationelectrical-pneumatic controls can be used. The float 54 communicateswith a transducer 55 which converts the position signal of the float toa pneumatic signal, with this signal being passed on to a leveltransmitter 55a and to a level` controller 54a. The level controller 54acommunicates with a flow recording controller 57 which also communicateswith a transducer 59. This transducer 59 is a conventional apparatuswhich converts a pressure differential from opposite sides of theorifice plate assembly 58 to a signal responsive to the pressuredifferential. A conduit is provided running from the flowrecorder-controller 57 through a 3-way valve 63 to the diaphragm of anormally closed diaphragm valve 61. This conduit is identified byreference numeral 62. The 3-way valve 63 is so installed in conduit 62that in one position control air pressure can pass through conduit 62 tothe diaphragm of motor valve 61 and in its other position this conduit62 is closed off and pneumatic pressure from the diaphragm of valve 61is vented through a vent 69.

The level transmitter 55a is operative only to a signal from transducer55 indicating a predetermined low liquid level in the presaturator 44.This level transmitter is connected operatively with areceiver-controller 56 which communicates with a diaphragm of the 3-wayvalve 63. This valve 63 is a normally vent valve, that is, when there isnot any pressure on its diaphragm, the valve is turned so that pneumaticpressure will vent from the diaphragm of valve 61.

A conduit 66 leads instrument air from a source, not shown, through a3-way valve 64 to the receiver-controller 56. This 3-way valve 64 isalso a normally vent valve venting pressure from the portion of conduit66 adjacent receiver-controller 56 by way of a vent 65.

This control apparatus is actually. a safety apparatus and operates insuch a manner that the steam turbine driven pump 34a will never removeall of the liquid absorbent from the kettle section of presaturator 44and go on gas. As will be realized by those skilled in the art, aturbine driven pump should never be permitted to go on gas because withno load on the pump the turbine will race with the result that theturbine and pump may be damaged.

In the operation of this apparatus, when the float 54 senses a normallow level for example, the signal therefrom is converted in transducer55 toi a pneumatic signal between, for example, 3 and 15 (p.s.i.g.)pounds per square inch gauge and this signal is -transmittedfto thelevel controller 54a which, in turn, emits a signal to reset the setpoint of the flow recorder-controller 57. This controller has previouslybeen set in order to regulate steam passing through conduit 60containing valve 61 to the turbine 34 to pump a predetermined volume ofabsorbent oil to the absorber 12. While it is desired to pump apredetermined and suitable volume of liquid absorbent into absorber 12there are times when less absorbent or more absorbent can be introducedinto the absorber without markedly upsetting the operation of theabsorber. Since it is desired not to have the pump 3411 go on gas, whenthe level sensed by float 54 reaches a level somewhat below the desirednormal liquid level, a signal is emitted from transducer 55 to the levelcontroller 54a. This level controller then resets the set point of theflow recorder-controller 57 thereby regulating the passage of instrumentair through conduit 62to the diaphragm of motor valve 61 in order tothrottle this motor valve 61 to reduce the flow of steam to the turbine.Thus, when the level of oil in saturator 44 decreases somewhat below thenormal desired working level, steam to the turbine is throttled so thatless oil is withdrawn from the presaturator. The reverse is true, thatis, if the level of oil in the kettle section of presaturator 44 risesabove the desired working level, the transducer emits a signalproportional to the rise of liquid level to the level controller 54awhich then resets the set point of controller 57 to open somewhat valve61 to speed up the turbine and pump.

When a dangerously low liquid level exists in the presaturator 44, thefloat 54 emits its signal to transducer 55 which in turn passes a signalto the level transmitter 55a. This signal is between 3 and 15 p.s.i.g.The receivercontroller 56 is a snap action on-otf controller and it canbe set to operate at, for example, 14 p.s.i.g. Thus, when thedangerously low liquid level in presaturator 44 is sensed by float 54with the continuous signal being emitted from transducer 55 to the leveltransmitter S511 and when the air pressure from transmitter 55a tocontroller 56 reaches 14 p.s.i.g., this controller snaps and cuts offflow of instrument air from conduit 66 to the diaphragms of the 3-wayvalves 63 and 64. Upon closing oif of this air, pressure is reduced onthe diaphragm in three-way valve 63 thereby allowing the normally ventvalve to vent pressure from the diaphragm of normally closed valve 61through vent 69. This venting thus closes oif all steam to the turbine34 and terminating all transfer of absorbent from the presaturator 44 tothe absorber 12.

As a double safety feature, the 3-way valve 64 has its diaphragm incommunication also with the outlet of the receiver-controller 56 so thatwhen this controller closes off the flow of instrument air to thediaphragm of 3-way valve 63 the instrument air to the diaphragm of the3- way valve 64 is also closed otf, thereby venting residual airpressure from the receiver-controller 56 by way of vent 65. At thistime, air from the portion of conduit 66 on the air source side isclosed off from entering the recorder-controller S6.

This last operation oceurs as mentioned hereinabove when the liquidlevel in presaturator 44 reaches a dangerously low level. With theturbine closed down then upon rise of the liquid level in presaturator44 above the dangerously low level mark, the instrument air pressureemitted by level transmitter SSa is reduced to a value below theabove-mentioned 14 p.s.i.g., thus the receivercontroller 56 snaps in theopposite direction but valve 64 is on vent and air from the sourcecannot pass through this valve to reach controller 56. Thus valves 63and 64 cannot return to normal operation. In order to start the turbine34, a bypass conduit 71 is provided around valve 64 in conduit 66. Amanually operable, push button valve 72 is placed in this bypassconduit. To flow steam to the turbine, merely push the valve button ofvalve 72 and air then flows to the receiver-controller 56. With thisinstrument having snapped open, pressure passes to the diaphragms ofvalves 64 and 63 opening both valves to air flow and closing the vents.As soon as valve 64 opens the push button is released and operation ofcontroller 56 is back to normal. With pressure on the diaphragm of valve63, this valve then admits pressure to the diaphragm of valve 61 therebyopening same to permit steam flow.

The check valve 67 is provided in conduit 33 to prevent back flow ofabsorbent or gas through conduit 33 into presaturator 44 when the pumpis not in operation. In one instance, the presaturator 44 was operatedat a pressure in the vicinity of 240 p.s.i.g., while the absorber wasoperated at a pressure somewhat above 1000 p.s.i.g. It is, thus,realized that the point of introduction of aborbent liquid by way ofconduit 33 into absorber 12 is in a normally gas or vapor contained areaand upon closing down of pump 34(1, what little liquid is in conduit 33will back flow into the presaturator, thus allowing gas at an extremelyhigh Velocity'to back flow through this conduit, therefore racing thepump 34a in a reverse direction. Such an irregular operation obviouslycan seriously damage pump 34a and the turbine 34.

As an example of the operation of such a system for the extraction ofgasoline from natural gas, are the following data:

Table Stream Name Gas to Abs. L O. to Presat. R.O. from S.V.T. 11.0.from Abs. Residue Presat. Oil to Abs. bs. Vapor S.V.T.

63 54 0 2 11 3 2 2, 435 2, 370 0 1 es 2 0 0 1 0 1 0 0 0 40, 091 36, 8420 406 3, 655 449 144 10,227 s 661 0 2, 332 3,898 1, 774 1, 292 4, 493916 0 143 3, 720 2, 066 2, 702 450 3 0 0 447 156 327 1, 120 1 0 0 1, 119348 846 283 0 O 0 283 61 234 261 0 0 0 261 53 218 127 0 0 0 127 16 11424 0 0 0 24 1 23 0 0 8, 885 8, 885 8, 885 129 8, 885

Deph. L O. from L O. to Inlet Gas R.O. from Reabs. Prcsat. Stream Name0.H.V Still Reabs to Reabs. Reabs. Residue Residue Stream No 27 29 37 4241 40 47 Float 54, transducer and level controller 5411, when combined,are a conventional liquid level controllertransmitter apparatus, such asthat manufactured by Fisher Governor Company, No. 2500-2516-24913. Thereceiver-controller 56 is also manufactured by said Fisher GovernorCompany and is advertised by that company as a receiver-controller 2506.The level transmitter SSa is also manufactured by the Fisher GovernorCompany and is similar to the portion 54x of the conventional liquidlevel controller. Both of the instruments 54a and 55a emit continuoussignals proportional to the signal received from transducer 55.Instrument 57 is a pneumatic set receiver flow recorder-controller, suchas one manufactured by Taylor Instrument Company and identified by thatcompany as No. 127RF137. The transducer 59 is specifically adifferential converter transmitter such as one manufactured byMnneapolis-Honeywell Company and identified by that company as No.292N7G4. The 3-way pneumatically operable valves 63 and 64 are suchvalves as No. 2VG140 and manufactured by Taylor Instrument Company.These valves are open straight through on high pressure and vent on lowpressure. The flow recorder-controllers 38 and 46 are conventional flowrecorder-controllers and such can be purchased from any of thehereinabove mentioned instrument manufacturing companies.

Conventional liquid level flow controllers, not shown, are employed toregulate the level of liquids in the bottom sections of the absorber 12,still 25, and reabsorber 39. The need for, installation -of and use ofsuch liquid level controllers is well understood by those skilled in theart.

A water Circulation system 24a, with air cooler, is provided for thedephlegmator to condense vapors of the absorption oil carried from still25 into the dephlegrnator 26.

While certain embodments of the invention have been described forillustrative purposes, the invention obviously is not limited thereto.

We claim:

In the method of operation of a gasoline plant wherein gasoline boilingrange hydrocarbons are extracted from natural gas in absorption zone byan absorbent liquid' medium which flows from a separating zone to apresaturation zone and then to the absoprtion zone and the unabsorbednatural gas is separately removed from said absorption zone, theimprovement which comprises passing said absorbent medium into saidabsorption zone from said presaturation zone by means of a steam turbineactuated pump having a flow rate of steam introduced into a valve andthen into the turbine proportionately regulated by means of a levelcontroller means and a flow recording and Controlling means having a setpoint varied responsive to a signal transmitted from said levelcontroller means, said level controller means being responsive to theliquid level of said absorbent medium in said presaturation zone, andWherein the flow rate of steam is further regulated by means of a secondcontrol means connected to the valve responsive to a second signalprovided thereto from said level control means representative of apredetermined low liquid level of said absorbent medium in saidpresaturation zone to terminate flow of steam to said steam turbine andthereby terminating the flow of absorbent to said absorption zone fromsaid presaturation zone.

References Cited by the Examiner UNITED STATES PATENTS 2,242,11O 5/41Carney 55-43 i 2,299,s3o 2,339,o26 2445,043 2,5:21233 8 Legatski et al55-43 X Mercer 202-160 Souders et al. 196-132 Latcham 55-43 Miller 55-43Donaldson 137-95 Kirby 137-97 Hunter 137-95 Cottle 202-160 Ryden 103-35Province 103-35 Russell 55-31 Nobles et al 103-35 X Tolin et al 202-16015 REUBEN FRIEDMAN, Primary Examner.

